Neil Armstrong, the first man on the Moon, has launched an unprecedented attack on President Obama’s plans to dismantle Nasa’s manned space exploration program – a move that will result in the loss of thousands of jobs.

The world’s best-known astronaut, who has traditionally avoided controversy and rarely seeks the limelight despite his feat 41 years ago, warned that Mr Obama risks blasting American space superiority on a “long downhill slide to mediocrity.”

The decision to cancel Constellation, the project to send astronauts to the Moon again by 2020 and Mars by 2030, was “devastating”, Mr Armstrong said in a powerful open letter to the President.

“America’s only path to low Earth orbit and the International Space Station will now be subject to an agreement with Russia to purchase space on their Soyuz – at a price of over $50 million per seat with significant increases expected in the near future – until we have the capacity to provide transportation for ourselves,” he said in the letter, which was also signed by Gene Cernan, the last man on the Moon, and Jim Lovell, commander of the ill-fated Apollo 13 mission in 1970.

“It appears that we will have wasted our current $10-plus billion investment in Constellation and, equally importantly, we will have lost the many years required to recreate the equivalent of what we will have discarded.”

He adds: “For The United States, the leading space-faring nation for nearly half a century, to be without carriage to low Earth orbit and with no human exploration capability to go beyond Earth orbit for an indeterminate time into the future, destines our nation to become one of second or even third-rate stature.

“While the President’s plan envisages humans traveling away from Earth and perhaps toward Mars at some time in the future, the lack of developed rockets and spacecraft will assure that ability will not be available for many years. “Without the skill and experience that actual spacecraft operation provides, the USA is far too likely to be on a long downhill slide to mediocrity.

“America must decide if it wishes to remain a leader in space. If it does, we should institute a programme which will give us the very best chance of achieving that goal.”

Mr Armstrong’s letter was one of two issued yesterday, both representing a major embarrassment for the President as he prepares to visit the Kennedy Space Centre in Florida tomorrow to defend his proposal to pull the plug on Constellation as part of a “bold new course” for Nasa.

In a separate appeal to the White House, 27 other retired astronauts, flight directors and former Nasa officials – including three more of the 12 men to have walked on the moon and some of the most distinguished figures in space history – complain that Mr Obama is setting Nasa on a course that is “wrong for our country” and “misguided”.

“For those of us who have accepted the risk and dedicated a portion of our lives to the exploration of outer space, this is a terrible decision,” they state.

“America’s greatness lies in her people: she will always have men and women willing to ride rockets into the heavens. America’s challenge is to match their bravery and acceptance of risk with specific plans and goals worthy of their commitment,” they added, estimating that up to 30,000 “irreplaceable engineers and managers” would be lost to the space industry after the shuttle retires later this year or early next if its successor is cancelled.

“One of the greatest fears of any generation is not leaving things better for the young people of the next. In the area of human space flight, we are about to realise that fear.

“Nasa’s human space programme has inspired awe and wonder in all ages by pursuing the American tradition of exploring the unknown. We strongly urge you to drop this misguided proposal that forces Nasa out of human space operations for the foreseeable future.”TIMES ONLINE